Semiconductor technology method of contacting a body



July 17 H. L. ARMSTRONG SEMICONDUCTOR TECHNOLOGY METHOD OF CONTCTING ABODY Filed April 2l, 1959 Matig 2! ma@ 5f mmm. 37...

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IN V EN TOR.

BYMMM United States Patent vi() 3,044,147 SEMICONDUCTOR TECHNOLOGYMETHOD OF CONTACTING A BODY Harold L. Armstrong, Kingston, Ontario,Canada, as-

signor to Pacific Semiconductors, Inc., Lawndale, Calif., a corporationof Delaware Filed Apr. 21, 1959, Ser. No. 807,857

Claims. (Cl. 29--25.3)

This invention relates to electrical devices, and more particularly to amethod for providing closely spaced electrodes in an electrical device.This invention also relates to electrical devices having closely spacedelectrodes upon at least one surface thereof.

It has long been desirable in the Asemiconductor art to producetransistors'capable of carrying relatively large currents. While thishas been accomplished in some instances by increasing the size of thesemiconductor body from which the transistor is manufactured, it remainsde- ,sirable to produce a transistor of relatively small size which hasa low base resistance and thereby is capable of carrying large currents.In order to accomplish this -it has been recognized that the emitterelectrode should have a substantial amount of contact with the baseregion and at the same time should be as closelyspaced to the baseelectrode as is physically possible.

A structurejto meet the above requirements has in the past beenattempted by alloying concentric rings of metal into the surface of thesemiconductor body from which the transistor has been made. Typicalexamples of such a structure may be found by referring to volume 45 ofProceedings of the I.R.E., page `544 in an article by N. AH. Fletcher,published in 1957. While devices having such a structure as abovedisclosed work quite well under "some circumstances, it has been foundthat it is exceed- Iingly diicult to control the close spacing betweenthe concentric contact rings. It has also been found that during thealloying step, the material which is being utilized to form adjacentrings has a tendency to dissolve 'laterally through the semiconductormaterial and cause the adjacent rings to come into contact with eachother, thereby shorting out the various regions of the transistor.

YIn addition to the above diiculties, when the concentric structure isutilized, and particularly when several of the narrow rings are requiredin order to obtain the desired amount of contact, it becomes necessaryto physically attach leads for electrical connection to' each of theconcentric rings which are alloyed to the semiconductor device. If agreat number of the rings are utilized, this necessitates additionalsteps in the process of manufacture, thereby greatly increasing the costof the device. If a large number of the rings are utilized, it becomesexceedingly diicult to make the proper electrical connections theretoand also causes the end product to be quite fragile. Furthermore, inconstructing such electrical devices as resistors and the like it oftenbecomes necessary to provide electrical contact to closely spacedregions of the device body. By using prior art techniques it isexceedingly diicult to obtain very close spacing of contacts and in somecases almost impossible.

Accordingly, it is an object of the present invention to provide amethod of making closely spaced contacts to a surface of an electricaldevice.

It is another object of the present invention to provide a method formaking semiconductor devices which are capable of carrying a relativelyheavy current. Y It is another object of the present invention toprovide a method for making semiconductor devices having electrodes moreclosely spaced than heretofore-possible, while at the same timeproviding a large amount of contact to the desired portions of thesemiconductor device.

It is yet another object of the present invention to pro- Mce vide amethodfor making more ecient high-current carrying capacity transistors.

It is still another object of thepresent invention to provide a methodfor making semiconductor devices having closely spaced electrodes whichprovide a large amount of contact to desired portions of the semicon-Zductor body and at the same time requires only a single connection toeach of the regions of the semiconductor device. Y l

It is a further object of the present invention to provide a method formaking transistors which have the emitter and base electrodes thereoflocated' upon fone sur' face of the transistor and spaced close to eachother.

It is a further object of the present invention to pro-l vide atransistor capable of carrying greater currents than heretofore possiblewith transistors of comparable size.-

It is yet a further object of the present invention to provide anelectrical device having closely spaced electrodes located on onesurface thereof.'

It is yet a further object of the present invention to provide atransistor having the emitter and base elec-y trodes closely spaced andlocated upon one major surface thereof.

In accordance with the method of the present invention; a layer ofelectrically conductive material is applied to a portion of one surfaceof a bod'y. The material is alloyed with the body to cause it topenetrate intothe body. An insulative layer of material is formed uponaprotrusion remaining at the body surface and thereafter a layer ofelectrically conductive metal is applied to the surface of the body andover the insulative layer.

Also in accordance with the present invention, a device includes a bodyhaving an electrically conductive material alloyed with at least aportion of one surface thereof. A layer of insulative material isprovided upon the alloy and a layer of metal is provided upon thesurface of the body and over the insulative material. f

More specifically, a junction-type semiconductor device in accordancewith the present invention includes first and second regions of oppositeconductivity type sepa;

rated by a P-N junction. A heavily doped region having a conductivitytype the same as the second region ex# tends through the first regionyand* tinto the second region and has a protrusion molecularly aixedthereto.. The protrusion has a layer of insulative material upon it. Alayer of metal is provided upon the surface of the body and over theinsulative layer. j

Other and more specific objects of the present invention will becomeapparent from a consideration of the following description taken inconjunction with the accompanying drawing, which is presented by -wayofvexample only7 and is not intended -as a limitation upon the nolvelfeatures of this invention which are .set forth in the appended claims,and in which: j

FIG. 1 is a cross-sectional view of a semiconductor device upon whichthe method of ther present invention is to be carried out;

FIG. 2 is a schematic representation of the function of the apparatuswhich may be used in practising the method of .the present invention;FIG. 3 is a top viewof a semiconductor device after the rst step in themethod ofthe present invention has been carried out; FIG. 4 is across-sectional view of .the semiconductor device as illustrated in FIG.3;

FIG. 5 is a cross-sectional view after the next succeed-A ing lstep ofthe method of the present invention has been carried out;

FIG. 6 is a cross-sectional view of a semiconductor device lafter eachof the steps of the present invention have been carried out;

FIG. 7 is a cross-sectional View illustrating a finished.

semiconductor device in accordance the present in-d vention;

FIG. 8 is a cross-sectional -view illustrating another ernbodiment of adevice in accordance with the present inxtention;andY .l'

FIG. 9 is a schematic representation of a semiconductor device asillustrated `in FIG. 6. Y Referring now to the drawing, land moreparticularly to FIG; l thereof, there is shown a semiconductortransistor generally designated as 10'Which includes `an emitter region11, ka base region 12, and a collector region 13. As illustrated, and byway of example, the transistor as shown is an N-P-N type transistor.

Although the semiconductor device as killustrated in FIG. l is atransistor of the N-P-N type, it should be expressly understood that themethod of the present inventionis applicable to many types of Ibodies towhich contact is to be made `and to transistors of the P-N-P type and.is as well applicable to other semiconductor devices such as diodes,thermistors, resistors, photocells, and the like. For purposes ofillustration only, the description of the method of the presentinvention will be described in connection with an N-P-N transistor ofthe silicon type. It should also be expressly understood that the methodof the present invention is applicable to semiconductor de- 'vicesconstructed from materials other than silicon. Examples of additionalmaterials lfrom which semiconductor devices may be made are germanium,germanium-silicon' alloys and the inter-metallic compounds such as, byVway of example only, gallium-arse'nide, indium-phosphide and the like.f f

The transistor as illustrated in FIG. 1, may be constructed by the wellknown diffusion process. For example, a P-type silicon body is placedwithin an open or closed tube type furnace. A gaseous medium isprovidedY in .the tube and around the semiconductor body. The gaseousmedium vwill contain an active impurity type material which will diffuseinto all surfaces of the semiconductor body and which will convert theexterior regions thereof to the opposite, or N-type, conductivity. 'Ihediffusion process has been fully' 'disclosed in the literature and iswell known to the art. i l,

The semiconductor body is then formed into the configuration as shown inFIG. l by removing the edgeportions thereof by dining, lapping, or thelike, thus, leaving first `and second regions of N-type conductivityseparated by an intermediateregion of P-type conductivity asillustrated. i Y f After formation of the transistor, a mask is thenplaced adjacent the emitter region thereof as illustrated at 14 in FIG.2, yto which referencey is hereby made.` 'Ilhe'masking material may beany which is .presently well known to the art, such as, for example,nickel, molybdenum,` tantalum, graphite, or the like. In the presentlypreferred embodiment voi this invention, nickel isutilizedas the maskingmaterial.` The masking material is constructed in such a manner thatopenings xare provided therein to expose a predetermined portionrofrthesurface of the semiconductor body upon which the mask -14 is placed.

After the mask 14 is in place adjacent the emitter region 11 ofthetransistor 10, the transistor is placed within an 4apparatus which isvadapted to apply jan electrically Vaofi/1,14*?

4 ductor-s For Signal Translating Devices, issued Novem# ber 30, 1954 toM. Sparks.

After the semiconductor body is positioned Within the apparatus asillustrated in FIG. 2, the electrically conductive Vmaterial is appliedthrough the openings in the maskrand upon the surface of the emitterregion 11 as illustrated by the arrows 16 extending from the source 15.In the presently preferred embodiment of the present invention whereinan N-P-N silicon transistor, as'illus trated in FIG. ll, is utilized,the electrically conductive material is a metal and preferably isaluminum.

The material which is`deposited upon or applied to the surface of theSemiconductor device must be capable of dissolving the particularsemiconductor material when heated in combination therewith. Althoughother metals such as bismuth and tin arecapable of dissolvingsemiconductor material, it has been found preferable in practicing thepresent invention to utilize aluminum which readily dissolvesbothsilifcon and germanium.

The aluminum is preferably applied to theY semiconductorV body by vapordeposition in a vacuum while maintaining the temperature of thesemiconductor body 1() above the eutectic temperature of aluminum andsilicon and preferably at approximately 800 C. In thel alternative, thealuminum may be applied by evaporating through the mask directly uponthe semiconductor body without raising the temperature of theVsemiconductor body. The temperature of the semiconductor body 10 israised to the desired level by applying a source of po-V tential to vtheheating device 17 to cause heat to be applied therefrom to thesemiconductor body 10 as illustrated by the lines 18 in FIG. 2. As longas an electrical potential is applied to the heating device 17, thetemperature of the semiconductor body 10 will be maintained at thedesired level.

After the aluminum is applied to the surface thereof,.

the temperature of the semiconductor body 101 is main-` tained in excessof the eutectic temperature of'silicon and lustrated the pattern whichthe evaporated aluminum' asconductive material through the openings inthe mask f l sumes Vafter passing through the openings in the mask 14onto the surface of the emitter region 11 of the transistor 10. As isillustrated in FIG. 3, the evaporated aluminum assumes a configurationsimilar to a bar having a series of elongated protrusions or fingersalong one surface. thereof and extending across a `major portion of thesurface of'the emitter region 11 of .the transistor 10.- Al# though fiveof these protrusions are illustrated in FIG. 3, one skilled in the artcan readily see that fewer or additional lringers may be utilizeddepending upon the particular application and the amount of current forwhich the transistor is being designed. It should also be understoodthat the evaporated aluminum may be deposited in discrete regions uponthe region 11 in order to form a series `of individual contacts to thebody. 'For the best results with reference to the current carryingcapacity of the transistor, the dimensions of each of the ngers shouldbe approximately one to twentymicrons in thickness and approximately oneto ten mils in width. I

The coniiguration'of material as illustrated at 21 in FIG. 3 may valsobeobtained, in addition to evaporation through a mask, by way of sprayingmolten valuminum onto the surface, or by pre-forming Va solid blank ofmaterial and placing this blank upon the surface of the semiconductorbody prior to heating the combination. It should also be expresslyunderstood that although the congura tion of the aluminum shown at 21 inFIG. 3 is the pre-V ferred embodiment in accordance with the method ofthe pres/ent invention, it may vary in accordance with any particulardesign configuration. For example, a bar of material could be providedacross the center of the tran# sistor with the fingers extending fromeach side thereof. Other configurations will become readily apparent tothose skilled in the art.

Referring now more particularly to FIG. 4, which is a cross-sectionalview taken along the line 4 4 of FIG. 3, it is seen that the aluminumhas penetrated into the semiconductor body as illustrated by dashedlines 23. As hereinabove described, this penetration is accomplished bymaintaining the temperature of the semiconductor body and the aluminummaterial deposited thereon at a temperature above the eutectictemperature of silicon and aluminum.

The temperature at which the combination of the aluminum and silicon ismaintained causes the aluminum to remain or become molten and todissolve portions of the silicon semiconductor body with which it is incontact. As the aluminum dissolves the semiconductor material, itpenetrates into the semiconductor body. The depth of penetration iscontrolled by the particular temperature and the amount of time duringwhich this temperature is maintained. As illustrated by the terminus 24of the dashed lines 23 in FIG. 4, the desired depth of penetration iscompletely through the emitter region 11 of the transistor and into thebase region 12 thereof. When applying contacts to a silicon transistorwhich is approximately one-half inch square and .O05 inch in thicknessand with the thickness of aluminum, temperature and time as above setforth, the amount of penetration as illustrated in FIG. 4 will occur.

After the desired penetration has been accomplished, the heat is removedfrom the silicon transistor and it is allowed to cool. Although the rateof cooling is not considered a critical parameter, it has been foundthat a cooling rate of approximately 0.2" C. per second givessatisfactory results. When this is done, a portion of the dissolvedsilicon precipitates from the molten aluminumsilicon solution andregrows onto the parent semiconductor body and in so doing follows thecrystalline planes present in the parent semiconductor body.. As thetemperature of the combination of aluminum and silicon goes below theeutectic temperature of silicon and aluminum, the remaining moltenportion of the aluminum-silicon solution freezes out as analuminum-silicon alloy which is predominantly aluminum.

The resulting structure as illustrated in FIG. 4 consists of a silicontransistor as illustrated in FIG. 1 with regions of very low resistivityP-type silicon material eX- tending through the emitter region and intothe base region as illustrated by the dashed lines 23 as shown in FIG.4. The low resistivity is a result of the use of aluminum as the metalwhich is deposited upon the sur- :face of the semiconductor body 1t).This aluminum is, as is well known in the art, an active impurity of theP- type which is capable of doping semiconductor material. If a lowerresistivity than that which is possible by 4utilizing aluminum isdesired, or if a metal other than aluminum is deposited from the source15 as hereinabove described upon the surface of the semiconductor body10, a material may be added which is a P-type active impurity, forexample, gallium, indium, aluminum, or boron from column III, of theperiodic table as arranged according to Mendeleev. In the alternative,if the method of the present invention is being carried out upon a P-N-Ptransistor, N-type active impurities such as phosphorous, arsenic,antimony, or bismuth from column V of the periodic table may be selectedand added to the material which is deposited upon the surface of thetransistor 10. Particularly, aluminum which is heavily doped with one ofthe N-type active impurities may be deposited upon the surface of aP-N-P transistor and the remaining steps of the method of the presentinvention carried out to provide the desired contact.

Since as hereinabove described, a very low resistivity region of P-typesemiconductor material extends into a P-type base region, an ohmiccontact occurs between the 6 low resistivity material and the originalbase region 12 of the transistor 10.

This contact would be constituted by that portion of the dashed line 23which extends into the base region 12 as illustrated by the dashedportion 24 thereof. ,Since the emitter region 11 is of sN-typeconductivity and the low resistivity region is of P-type conductivity, arectifying contact is established between these two areas.

It is, therefore, seen that to provide the desired contact the lowresistivity region that is formed must have the same conductivity typeas the base region and opposite conductivity type to that of the emitterregion.

Under certain circumstances during the practice of the method of thepresent invention, it is possible that the molten alumin'urri maypenetrate completely through the base region and contact the collectorregion. If this should occur, the resulting device would be operativesince a rectifying contact would occur between the low resistivityP-type region and the N-type collector region of the transistor. Foroptimum results, however, this should not be allowed to occur since itwill decrease the amount of contact between the low resistivity regionand the base region of the transistor, thereby decreasing the amount ofvoltage which can be supported by the contact structure.

In accordance with the foregoingsteps of the method of the presentinvention, a large amount of contact has now been provided to the baseregion and is brought present invention as hereinabove described may beillus' trated schematically as shown in FIG. 9 to which reference ishereby made. As therein shown the transistor includes an N-type emitterregion' 41, a P-type base region 42 and an N-type collector region 43. Ajunction 46 separates the base region 42 and the collector region 43.` Ajunction also separates the base and emitter regions but it may beviewed in a slightly different'manner. It should' be recalled that themetal which is applied to the surface of' the emitter region is causedto penetrate through the Vemitter region and into the base region tothereby provide a base contact at the surface' of the device. This mayalso be looked upon as causing the base region 42 to extend in an upwarddirection through the emitterregion 41 and to the surface of the deviceas shown at 44. The base region 42 therefore includes upwardly extendingportions 44 as shown in FIG. 9; Such a lstructure clearly increases thecontact surface be-y tween the emitter and base regions. The junctionseparating the emitter and base region is then as shown at 47. Theextended portions 44 of the base region 42 are heavily doped and of lowresistivity as above described which is designated by the P+ appearingtherein. The P-jportion extends into the base region 42 as shown bydashed lines 45 to accomplish the desired contact therewith. Inoperation of a device of this type a slightly higher barrier will existbetween the N region 41 and the P| portion 44 of the emitter-basejunction than between the N region 41 and the P-type main portion of thebase.

Referring now more particularly to FIG. 5, there is illustrated the`structure of FIG. 4 and in addition a layer of insulative material 31is provided upon the aluminum rich alloy material 21 extending above thesurface of they emitter region 11 of the `transistor 10. As isillustrated in FIG. 5, this region is in tlhe physical configuration ofa protrusi-on above the surface of the transistor.

In accordance with the preferred embodiment of the present inventionwhere aluminum is evaporated upon ya silicon transistor, this insulativelayer may be aluminum' order to form the base electrode to thetransistor 10, the

insulative layer may be provided in other manners. YFor example,insulating material may be applied which completely. covers the metallicprotrusions extending above the surface of a semiconductor' body. Suchinsulatinglmaterial may be applied for example, through a mask, bypainting, or other well known methods.

Auber the formation of the insulative layer such as the oxide layer 31of FIG. 5, Ithe next step in the method fof the present invention is toprovide an electrically conductive layereof material Vupon the exposed oemitter portions of the .transistor 10.` Such a layer of material is 'asillustrated inFIG. 6. The electrically conductive material which isillustrated at 32 in FIG. 6, may be applied ltdthe emitter region 11 ofVthe transistor 10 by evaporating fthe material 32 upon substantiallythe entire surface of thesemi-conductive body including the protrusionshaving the insulative ymaterial 311 thereo'ver. Any suitable materialmay be utilized to provide the layer 32 which is electrically conductiveand which will provide godlohmi-c contact to the surface of .the emitterregion 11:. The semiconductor body is preferably `heated duringthis,evaporation.Y InV thealternative, l-ayer of material 32 m'ay beapplied lupon :the surface by means well known to the art other thanevaporating such as electroless plating, 'chemicalV reduction, land thelike. Types of material which may be utilized and which meet therequirements for 'the emitter `Contact material .32 are for example,silver, gold, nickel, copper, Vand the like, or

, combinations thereof.A

,.'Afterltheformation `of the emitter electrode las illustrated in FIG..6,l the only step remaining to provide a completed transistor isntheattachment of lthe electrical ledsftoV the variousportions ofthetransistor. This is as illustratedin FIG. 7. Qhmc contacts are made asillus'- trated 'at 53 so l'die collector region, at 54 to the emitterregion, k1and at `V55 to the base region. vl'hese ohmic *contacts maybemade by any' well-knownm'ethod such as menno-'compression bonding,soldering,Y or the like. AAs noted,`in 'order to maketh'e base leadSScontact the base electrode a portion 'of the 'material 3l?. which hasbeen applied in "-orlder to form theemitter electrode, together with acorresponding Yportion of the underlying insulativ'e material '31, mustbe removed from one of the protrusions f21 'in order to allow contact tobe lmade thereto. This l'may be accomplished by ab'radi'rig 'thatportion or infth'ealternative', by applyinga small mask to thejdesiredaeaprior 'tothe deposition of the materials 31 and 32t It will be notedthat 4the lspacing between the emitter and 'the .base electrodes is'exceedingly 'close' and is de-V termined only by the thickness of theinsulative layer 31 which vis applied as illustrated in FIG.` 5. lTherefore, spacing between emitter and base electrodes of approximately.0002 inchis readily yaccomplished`in"accorda.uce with the method' ofthe present invention, thereby providing a transistor which will giveoptimum results.

Referring now to FIG. 8, there'is 'illustrated a body 33 of P-typesemiconductor material which may be used as a'zresistor or Vthe like.Contacts to portionsof the body 33 have been made by yalloying a metalthereto as hereinabove described and as illustrated at 34 to provide aregion of like conductivity type.V VThe alloying has providedohmiccontact to the Ibody 33 illustrated by dashed linesm3l.V`insulativelayer of material 35 'is provided over the pro-trusions 34 andm-ay be aluminum oxide.v A layer 36 of conductive metal is then placedover the entire surface of the body 33 including the insulative oxidevlayer to provide electrical contact directly to body 33. Suchaconguration provides contact to very closely spacedy portions of thebody, the contacts provided by the alloy 34 and the metal layer 36 beingseparated by the insulative layer Y35,. Leads may then be applied to thealloy regionw34 and to the conductive metal layer Saas above describedto provide the completed device. l There has been thus disclosed amethod for making a device having closely spaced electrodes and there isas well disclosed a transistor and a semiconductor body having closelyspaced electrodes on at least one surface thereof. Y Y

What is claimed is:

l. The method of providing closely spaced contacts upon atleast onesurface of a body, said method comprising the steps of: applying acontact to one surface of a body; providing a layer of insulativematerial upon said contact; applying a layer of electrically conductivematerial upon said one surface and over said insulative layer; removinga predetermined portion of said layer of electrically conductivematerial and of said insulative layer to expose a surface of saidcontact; and, ohmically bonding an electrical lead to said exposedsurface of said contact.

The ymethod of providing closely spaced contacts upon'at least onesurface of a semiconductor body, said method comprising the steps of:alloying an electrically conductive material with at least a portion ofone surface of a semiconductor body, forming a layer of insulativekmaterial only upon that portion of said alloyed material ertnding abovesaid one surface; and applying a layer of electrically conductivematerial upon said surface and over said insulative layer.

3. The method of providing closely spaced contacts upon at least onesurface of a semiconductor body, said methd'cornpri'sing the steps of:alloying aluminum with at least a portion of one surface of asemiconductor body, forming a layer of aluminum oxide upon said alloy,and applying a layer of electrictrically conductive material upoufkfsaidsurface and oversaid oxide.

44. 'Ihe .method of providing closely spaced contacts upon one majorsurface of a semiconductor body, including yfirst and second regions ofopposite conductivity type separated by a P-N junction, said methodcomprising uthe steps of: applying a solvent metal t0 a predeterminedportion of said surface; heating the combination to cause -said solventmetal to penetrate throughv said first region and into said secondregion; cooling the combination to provide an area of said solvent metalat said surface and an ohmic contact with said second region and arectifying contact with said first region; providing an insulativcmetallic composition upon said area of said sol-vent metal; and applyinga layer of electrically conductive material upon substantially theentire area of said surface.

`5. The -m'ethod of providing closely spaced electrodes for-asemiconductor body containing a P-N junction, said method comprising thesteps of .providing a semiconductor body having'at least a region of oneconductivity type separated Yfrom a region of the opposite conductivityby a P-'N junction; applying a solvent metal containing conductivitytype determining atoms 'of said opposite conductivity type to apredetermined portion of said one conductivity type region of saidsemiconductor body, heating the combination to a temperature to causesaid solvent metal to penetrate through said one vconductivitytype'region andirto ysaid opposite conductivity Vtype region; coolingthe combination to provide Yan area consisting predominantly of saidsolvent mtal 'upon said semi-conductor body; providing an iusulativeoxide layer upon fsaidsolvent metal area; and depositing a layer ofelectrically conductive metal upon said one conductivity type region ofsaid semi-conductor body.

6. The method of providing closely spaced contacts upon one majorsurface of a semiconductor body, including rst and second regions ofopposite conductivity type separated by a P-N junctiomsaid methodcomprising the steps of: applying aluminum to a predetermined portion ofsaid surface; heating the combination to cause said aluminum topenetrate through said first region and into said second region whileretaining an area consisting predominantly of aluminum at said surface;cooling the combination; providing a layer of aluminum oxide on gsaidarea of aluminum; and applying a layer of electrically conductive metalupon said surface and over said aluminum oxide.

7. The method of providing close spaced emitter and base electrodes onN-P-N transistors comprising the steps of: providing an N-P-N transistorhaving emitter, base, and collector regions; depositing a layer ofaluminum upon predetermined portions of the emitter region of saidtransistor; heating the combination to a temperature above the eutectictemperature of said transistor and said aluminum to cause said aluminumto dissolve a portion of said transistor; maintaining said temperatureabove the eutectic temperature for a time sufficient to permit saidaluminum to penetrate into said transistor and at least contact saidbase region; cooling the combination to provide an area on a portion ofsaid. emitter region consisting predominantly of aluminum; anodizingsaid area of aluminum to provide a layer of aluminum oxide thereuponhaving a thickness of the order of 0.2 mil; depositing a layer ofelectrically conductive metal upon said emitter region including saidalurm'num area; and attaching leads to said aluminum area and said metallayer to provide base and emitter leads, respectively for saidtransistor.

8. The method of providing closely spaced contacts upon one majorsurface of a silicon semiconductor body including first and secondregions of opposite conductivity type separated by a P-N junction, saidmethod cornbase contacts upon one major surface of a silicon transistorhousing iirst and second regions of N-type conductivity separated by anintermediate region of P-type conductivity, said method comprising thesteps` of: providing a mask adapted to expose a predetermined areaadjacent said surface of said silicon transistor; vapor depositingaluminum through said mask and upon said surface of said silicontransistor; heating the combination to a temperature exceeding thesilcon-aluminum eutectic temperature to cause the aluminum to penetratethrough said iirst N-type region and into said intermediate P-typeregion; cooling the combination to provide an area consistingpredominantly of aluminum upon said surface of said silicon transistor;treating said transistor to provide a layer of aluminum oxide upon saidaluminum area; and depositing an electrically conductive layer of metalupon said surface and over said aluminum area.

1.0. The method of providing closely spaced emitter and base electrodesupon one major surface of a silicon transistor having N-type emitter andcollector regions separated by a P-type base region, said methodcomprising the steps of: applying a photo emulsion to said surface ofsaid silicon transistor; exposing a predetermined portion of saidemulsion; removing the unexposed portion l@ t Y of said emulsion fromsaid surface; vapor depositing aluminum upon said surface of saidsilicon transistor; etching said transistor to remove that portion ofaluminum which covers said exposed emulsion along with said emulsion;heating said transistor and said aluminum tol a temperature exceedingthe silicon-aluminum eutectic temperature to cause the aluminum topenetrate through the emitter region and into the base region; coolingthe combination to provide an area consisting predominantly of aluminumupon said surface and to provide an ohmic contact with said base regionand a rectifying contact with said emitter region; treating at leastsaid surface to provide a layer of aluminum oxide upon said area ofaluminum; and depositing a layer of electrically conductive metal uponsaid surface and .over said aluminum area.

l1. The method of providing closely spaced contacts upon at least onesurface of a semiconductor body, said method comprising the steps of:molecularly bonding an electrically conductive material to apredetermined surface portion of a semiconductor body forming a layer ofinsulative material upon said electrically conductive material, andapplying a layer of electrically conductive material upon the surface ofsaid semiconductor body and over said insulating layer.

12. The method of providing closely spaced contacts upon at least onesurface `of ia semiconductor body, said method comprising the steps of:alloying an electrically conductive material with at least a portion ofone surface of a semiconductor body, forming a layer of insulativematerial only upon that portion of said alloyed material extending abovesaid one surface, applying a layer of electrically conductive materialupon said surface and over said insulative layer, removing apredetermined portion of said layer of electrically conductive materialand of said insulative layer to expose a surface portion of said alloyedelectrically conductive material, and bonding an electrical lead inohmic contact with said exposed surface portion of said electricallyconductive material.

13. The method of providing closely spaced contacts upon at least onesurface of a semiconductor body, said method comprising the steps of:alloying aluminum with at least a portion of one surface of asemiconductor body, forming a layer of aluminum oxide upon said alloy,applying a layer of electrically conductive material upon said surfaceand over said oxide, removing a predetermined portion of said layer ofelectrically conductive material and of said layer of aluminum oxide toexpose a surface portion of said alloyed aluminum, and bonding anelectrical lead in ohmic contact With said exposed surface portion ofsaid alloyed aluminum.

14. The method of providing closely spaced contacts uponrone majorsurface of a semiconductor body, including rst and second regions ofopposite conductivity type separated by a P-N junction, said methodcomprising the steps of: applying a solvent metal to a predeterminedportion of said surface; heating the combination to `cause said solventmetal to penerate through said first region and into said second region;cooling the combination to provide an area of said solvent metal at saidsurface and an ohmic contact with said second region and a rectifyingcontact with said first region; providing an insulative metalliccomposition upon said area of said solvent metal; applying a layer ofelectrically conductive material upon substantially the entire area ofsaid surface; removing a predetermined portion of said layer ofelectrically conductive material and of said insulating metalliccomposition 'to expose a predetermined surface portion of said solventmetal; and, bonding an electrical lead in ohmic contact with saidexposed surface portion of said solvent metal.

l5. The method of providing closely spaced contacts upon one majorsurface of a semiconductor/body, in-

cluding first and second regions of opposite conductivity type separatedby a P-N junction, said method comprising vthe steps of: applyingaluminum to a predetermined portion of Vsaid surface;heating thecombination to cause said aluminum to penetrate through said firstregion and into said second region While-retainngan area consistingpredominantlyof aluminum at said surface; cooling the combination;providing a layer of aluminum oxide on said area ofaluminum; applying alayer of electrically conductive metal upon said surface and over said`aluminum oxide;` removing a predetermined portion of said layer ofelectrically conductive metal and of said aluminum oxide to expose asurface portion of said aluminum; and,

bonding an electrical lead in ohmic contact with said exposed surfaceportion of said aluminum.

References Cited in the le, of'this patent UNITED STATES PATENTS Deyrupet al Nov. 27, 1945 Mathews et al Sept. 29, 1953 Fuller Dec. 21, 1954Ross Nov. 25 1958 Jones et al Dec. 23, 1958 Durst et al f Apr. 26, 1960

